1. Field of the Invention
The present invention relates to an image forming apparatus and the like, in which a color table (color conversion table) is constructed according to a kind of recording material. More specifically, the present invention relates to the image forming apparatus outputting a vertical synchronizing signal of an image signal required for outputting image data in consideration of a time required for color table construction, and to a method for controlling the image forming apparatus.
2. Description of the Related Art
FIG. 1 is a block diagram showing a configuration of a laser printer as an image forming apparatus.
In FIG. 1, the image forming apparatus includes an image forming unit 100, paper feeding units 20a and 20b (reference numeral 20a denotes a main body paper feeding unit and reference numeral 20b denotes an external paper feeding unit), and image fixing units 10a and 10b. 
Configuration of Image Forming Unit
First, a configuration of the image forming unit 100 will be described briefly.
The image forming unit 100 includes photosensitive drums 1a to 1d, which are four image bearing members, and charging means 2a to 2d in a circumference of the photosensitive drums 1a to 1d for uniformly charging the surfaces of the photosensitive drums 1a to 1d sequentially, according to a rotation direction. Moreover, the image forming unit 100 includes exposure means 3a to 3d for forming an electrostatic latent image on the photosensitive drums 1a to 1d by irradiating laser beams based on image information. In addition, the image forming unit 100 includes developing means 4a to 4d for attaching toner to the electrostatic latent image to be developed as a toner image, and transfer members 5a to 5d for transferring the toner images on the photosensitive drums 1a to 1d to a recording material. Furthermore, the image forming unit 100 includes cleaning means 6a to 6d or the like for removing toner after the transfer of the toner, which is residual on the surfaces of the photosensitive drums 1a to 1d after the transfer. Here, the photosensitive drums 1a to 1d, the charging means 2a to 2d, the developing means 4a to 4d, and the cleaning means 6a to 6d are integrally formed as a cartridge so as to form process cartridges 7a to 7d. On the other hand, feeding units 20a and 20b supply the recording material to the image forming unit 100. The recording material fed from the paper feeding units 20a and 20b is conveyed to the image forming unit 100 by a transfer conveyer belt 9, which is a transfer conveyer belt. Next, the toner image in each color is sequentially transferred to the recording material so that a multicolor image is formed. Next, the recording material is thermally fixed with the toner image by a fixing belt 10a and an elastic pressure roller 10b, and is discharged to and loaded on a discharging unit 13 by a pair of discharging rollers 10.
Next, the configuration and operation of the image forming unit 100 will be described in detail.
The photosensitive drums 1a to 1d as image bearing members are configured by applying an organic photo conductor (OPC) layer onto an outer circumferential surface of an aluminum cylinder. The photosensitive drums 1a to 1d are rotatably supported at both ends thereof by a flange, and are rotary-driven counterclockwise in relation to the figure by receiving driving force from a driving motor (not shown) at one end.
Each of the charging means 2a to 2d is a conductive roller formed in a roller shape, and uniformly charges the surfaces of the photosensitive drums 1a to 1d by causing each of the charging means 2a to 2d to abut on the surfaces of the photosensitive drums 1a to 1d, and by concurrently applying a charge biasing voltage from a power source (not shown) thereto.
Each of the exposure means 3a to 3d has a polygon mirror, and image light corresponding to an image signal is irradiated from a laser diode (not shown) to this polygon mirror.
The developing means respectively adjoin toner storing units 4a1 to 4d1, in which each color of black, cyan, magenta, and yellow is stored, and the surfaces of the photosensitive elements. The developing means is configured of developing rollers 4a2 to 4d2 and the like for carrying out development by being rotary-driven by the driving unit (not shown), and by being applied of a development biasing voltage from a development biasing power source (not shown).
Inside the transfer conveyer belt 9, the transfer members 5a to 5d, which touch the transfer conveyer belt 9, are respectively attached so as to be opposite to the four photosensitive drums 1a to 1d. The transfer members 5a to 5d are connected to a transfer biasing power source (not shown), and a positive electric charge is applied from the transfer members 5a to 5d to the recording material through the transfer conveyer belt 9. With this electric field, each color of toner images of a negative electric charge on the photosensitive drums 1a to 1d is sequentially transferred to the recording material, which is in contact with the photosensitive drums 1a to 1d, so that a multicolor image is formed.
Next, the operation of conveying the recording material in the image forming unit 100 will be described in detail.
The recording material fed to the image forming unit 100 from the feeding units 23a and 23b in the paper feeding units 20a and 20b passes through an interstice between an intermediate conveyer roller 23a and a resist roller 15. A recording material kind determining sensor 12 is provided between the intermediate conveyer roller 23a and the resist roller 15. The recording material kind determining sensor detects a kind of recording material passing therethrough. After the kind of recording material is detected by the recording material kind determining sensor 12, a recording material conveyance speed is changed to a speed for the recording material, and the transfer conveyer belt 9 conveys the recording material to the image forming unit 100 at the changed speed.
The transfer conveyer belt 9 as a recording material carrier is supported by three rollers, which are a driving roller 9b and driven rollers 9c and 9d, in a tensioned condition, and is disposed opposite to all of the photosensitive drums 1a to 1d. The transfer conveyer belt 9 is moved in circle by the driving roller 9b so that the recording material is brought into contact with the photosensitive drums 1a to 1d by sucking the recording material electrostatically onto the outer circumferential surface opposite to the photosensitive drums 1a to 1d. With this, the recording material is conveyed to a transfer position by the transfer conveyer belt 9, and the toner images on the photosensitive drums 1a to 1d are transferred onto the recording material. In addition, in the most upstream position of the transfer conveyer belt 9, there is disposed a suction roller 9e which supports the recording material by holding the recording material between the adsorption roller 9e and the transfer conveyer belt 9, and which causes the recording material to be sucked on the transfer conveyer belt 9. At the time of conveying the recording material, a voltage is applied to the suction roller 9e to form an electric field with the driven roller 9c provided opposite to the suction roller 9e. Accordingly, dielectric polarization is generated between the transfer conveyer belt 9 and the recording material so as to generate electrostatic suction force thereon.
Configuration of Image Fixing Unit
A fixing unit is to fix the toner image by applying heat and pressure to an image formed on the recording material, and includes a fixing belt 10a and an elastic pressure roller 10b. The elastic pressure roller 10b faces the fixing belt 10a with a predetermined pressure contact force with a belt guiding member to form a fixing nip portion N with a predetermined width. In a state where the fixing nip portion is heated up to a predetermined temperature, which then is controlled, the recording material, which is conveyed from the image forming unit 100, and on which toner image is formed, is inserted between the fixing belt 10a and the elastic pressure roller 10a of the fixing nip portion N, in a state where the image side is faced up. That is, the recording material is inserted facing the fixing belt side. Next, in the fixing nip portion, the recording material is conveyed together with the fixing belt 10a in a state where the image side of the recording material is appressed against the outer surface of the fixing belt 10a. In the fixing nip portion N, in a process where the fixing belt 10a and the recording material are conveyed together, the fixing belt 10a heats the fixing nip portion so that the toner image on the recording material is thermally fixed.
Configuration of Feeding Unit
When image formation is performed from the main body feeding unit 20a, the recording material is separately fed one by one by a cassette pick-up roller 21a, and the recording material is conveyed to the transfer conveyer belt 9 by the resist roller 15 by way of the cassette conveyance roller 22a and the intermediate conveyance roller 23a. When image formation is performed by feeding the recording material from the outer paper feeding device 20b, the recording material is separately fed one by one by a pick-up roller 21b of an optional paper feeding device. Next, the recording material is conveyed to the transfer conveyer belt 9 by the resist roller 15 by way of the conveyer roller 22b and intermediate conveyer rollers 23b and 23a of the optional paper feeding device.
Entire Configuration of Controlling System of Image Forming Apparatus FIG. 2 is a block diagram showing an entire configuration of a controlling system of the image forming apparatus of FIG. 1.
According to FIG. 2, this controlling system includes a host computer 200, a controller 201, and an engine controlling unit 202. The engine controlling unit 202 includes a video interface unit 210, a CPU 211, an image processing GA 212, an image controlling unit 213, a fixing controlling unit 214, a paper conveyance unit 215, a drive controlling unit 216, a double face controlling unit 217, and a recording material kind detecting unit 218, and controls each of the above-described elements.
The controller 201 is capable of intercommunication with the host computer 200 and the engine controlling unit 202 (respective signal lines 219, 220 and 221). The controller 201 receives image information and a print instruction from the host computer 200 through the signal line 219. According to the print instruction, the controller 201 transmits a print reserving command and a print starting command to the engine controlling unit 202 through the signal line 220.
When the print starting command is received, the engine controlling unit 202 starts paper feeding operation in the paper feeding unit, and conveys the recording material to a position where the recording material kind determining sensor is disposed between the intermediate conveyance roller 23a and the resist roller 15. The engine controlling unit 202 then stops the conveyance to detect a kind of recording material, and restarts conveying the recording material after detecting the kind of recording material. Then, the engine controlling unit 202 outputs a vertical synchronizing signal (/TOP signal), which is an instruction signal for outputting image data, to the controller 201 through the signal line 221.
The controller 201 analyzes image information received from the host computer 200 through the signal line 219 to convert the information into bit data, and constructs a color table to output the image data to the engine controlling unit 202 through the signal line 220, the image data being outputted in synchronization with the vertical synchronizing signal. The color table is a table for converting the bit data into a device color space, and further converting the device color space into CMYK by color separation.
Conveyance Operation of Recording Material and the Like
FIG. 3 is a schematic diagram for describing recording material conveyance at the time of printing operation. FIG. 4 is a flowchart for describing processing cooperatively performed by the controller 201 and the engine controlling unit 202 as a conventional example.
According to FIG. 4, the controller 201 designates, to the engine controlling unit 202, print conditions, such as a print mode instruction and a paper feeding port (20a) (S401 and S402). Next, the controller 201 transmits a print reserving command (ID1) and a print starting command (ID1) for each recording material (S403 and S404).
When the print starting command is received from the controller 201, the engine controlling unit 202 carries out printing preparation based on the designated print information (S405), and picks up paper from the paper feeding port 1 (20a) with the print mode (for example, a print mode for plain paper) corresponding to the kind of recording material, which is set in advance (hereinafter referred to as “an assumed kind of recording material”), so that paper feeding operation starts (S406, FIG. 3A). The engine controlling unit 202 performs detection of a kind of recording material at the time when the fed recording material reaches a position where the kind of recording material is detected (S407, FIG. 3B), and the detection result is notified to the controller 201 (S408). The engine controlling unit 202 performs switching to image forming conditions, which are optimal for the detected kind of recording material, after detecting the kind of recording material when needed, and outputs the vertical synchronizing signal for outputting the image data to the controller 201 (S411, FIG. 3C). The controller 201 constructs a color table for ID1 corresponding to the kind of recording material notified from the engine controlling unit 202 at S408 (S412), and then outputs the image data in synchronization with the vertical synchronizing signal from the engine controlling unit 202.
It should be noted that, in Japanese Patent Laid-open Application No. S06-62249, there is disclosed a device for detecting the kind of recording material, on which an image is formed, to switch a table value and the like of color converting means corresponding to the detected kind of recording material. According to this device, color reproduction consistent with an original copy is made possible with any kind of recording material used when image formation is performed. Furthermore, in Japanese Patent Laid-open Application No. H06-54117, there is disclosed a device which changes the density of color data registered in the color table at once. According to this device, efficiency of processing time and reduction of transferring data can be promoted, and a load of switching processing after the color table is registered can be reduced further.
In the above-described conventional technologies, however, the controller 201 constructs the color table as color converting processing data for the image data after the engine controlling unit 202 detects the kind of recording material. The image forming operation, therefore, has to be suspended during the time of constructing the color table after the recording material is fed and the kind of recording material is detected. This results in a situation where a time required for image formation becomes longer (because a waiting time until the image formation starts is required).
The color table needs to be constructed in accordance with the kind of recording material (plain paper, thick paper, thin paper, glossy paper, and the like), and a time required for constructing the color table according to the kind of recording material varies. Thus, when image forming operation is suspended as described above, the configuration is set up to be controlled so as to be suspended for a maximum time required for constructing the color table. A time required for image formation, therefore, becomes longer.
Here, it can be considered that the color table is constructed for each kind of recording material, and is recorded in advance in a non-volatile memory or the like in the controller 201. However, because there are many kinds of recording materials, a capacity of the non-volatile memory needs to be larger if color tables corresponding to all kinds of recording material are constructed and recorded therein. This results in increase of the costs. For this reason, from the viewpoint of keeping down the costs, it is preferable that the color table be constructed after the recording material is detected.
In contrast, when the engine controlling unit 202 outputs the vertical synchronizing signal to the controller 201 without considering the time required for the controller 201 to construct the color table, there arises a situation where image formation is not performed correctly. In other words, because the vertical synchronizing signal is outputted from the engine controlling unit 202 to the controller 201 before the color table construction is complete, the controller 201 cannot output the image data. As a result, there arises the situation where image formation is not performed correctly.